Gram-negative sepsis is a very common type of bacterial infection, particularly in burn victims and in patients treated with high doses of cancer chemotherapeutic agents for leukemia or other forms of cancer. There are several reasons for postulating that lipopolysaccharide, or endotoxin, in the cell wall of invading Gram-negative bacteria is an important factor in mortality. Despite the use of potent antibiotics and aggressive support techniques, there is still a high frequency of death.
Lipopolysaccharide has three portions: the oligosaccharide side chains; the core polysaccharide; and lipid A, which is considered to be the toxic moiety. Antibody to complete polysaccharide is directed primarily against the side chains, which differ widely from strain to strain. Therefore, antiserum to a complete polysaccharide is less likely to have protective activity against a broad range of bacterial strains. However, there is much less strain variation in lipid A than in the side chains. The core regions of most Gram-negative bacteria contain similar lipid A units. Antibodies to the core structure should, therefore, provide a broader scope of protection.